The present invention broadly relates to steering roll or caster arrangements and, more specifically, pertains to a new and improved construction of a resiliently mounted, pivotable steering roll or caster arrangement, especially for driverless vehicles.
In its more particular aspects, the present invention pertains to a resiliently mounted, pivotable steering roll or caster arrangement for a vehicle, especially for a driverless guided conveying vehicle, for mounting at the front and rear of the vehicle as viewed in the travel direction of such vehicle. The vehicle thus contains a front caster, i.e. a caster instantly assuming a front position as viewed in the instant travel direction of the vehicle, and a rear caster, i.e. a caster instantly assuming a rear position as viewed in the instant travel direction of the vehicle.
In other words, the present invention relates to a vehicle having a first travel direction and a second travel direction relative to a travel surface. The vehicle comprises at least one steering roll or caster arrangement and support means for pivotally mounting the at least one caster relative to the vehicle. The support means comprises suspension means for resiliently suspending the at least one caster such that the at least one caster can perform motion in a direction relative to the vehicle body.
At least three wheels of a remotely controlled or driverlessly guided industrial conveying vehicle driven by two drive wheels located in the middle of the vehicle body must be continuously held in firm contact with the ground. This can be conventionally achieved by providing at least one caster which is resiliently connected with the vehicle body. For a vehicle with more than three wheels this can only be ensured if jolts arising when a vehicle is guided over an uneven track or travel surface can be absorbed while at least three of the wheels simultaneously remain in firm contact with the floor or travel surface and the drive wheels exert an approximately equal force on the floor or travel surface.
In order that such industrial conveying vehicles can be employed unproblematically and in an operationally reliable manner even on conventional industrial floors, the resiliently mounted casters require a suspension displacement which is as large as possible at the front and rear of the vehicle. Such suspension displacements are provided by resilient mountings or suspensions which usually comprise a plurality of stages in order that the casters even of unloaded vehicles continuously touch, i.e. remain in intimate contact with the floor and therefore reliably adjust to the direction of travel. During an emergency stop caused or initiated, for example, by a collision protection device detecting or colliding with an obstacle, the upper part of the vehicle containing the payload tends to continue to move in the direction of vehicle travel. Before the braked center-mounted drive wheels come to a halt, the vehicle pitches or dips forward around the center-mounted axle or axis of the drive wheels. The suspension of the front caster thus is fully loaded and the front part of the vehicle dips downwardly together with the load. If the load which usually comprises individual packages or cartons stacked in layers on pallets, has not been secured very carefully by means of straps, the front upper layer of the packages or cartons may fall off the vehicle.
In a driverless guided vehicle having pivotable free-running casters such as known, for example, from U.S. Pat. No. 4,515,235, granted May 7, 1985, a suspension is provided between the front and rear freely running casters and the vehicle body. The vehicle body is tiltable in the direction of travel around the two drive wheels located along the middle of the vehicle body. The pitching or tilting motion is taken up by the front and rear casters which are interconnected and pivotably connected to the vehicle body by a horizontal lever arm and by a horizontal pivot pin supported at the center of the vehicle body by two mounting plates. The front and rear casters are resiliently supported at the vehicle body by related vertically arranged coil springs. In a particular embodiment of this vehicle, the vehicle body is displaceably mounted in a vertical direction by a splined shaft guided by bearings in each of a front and a rear splined hub. In this same embodiment, the vehicle body is supported by respective spring or suspension means or units at the front and rear casters. Vertical movements brought about by unevenness or irregularities in the floor or travel surface are taken up at each end by a respective coil spring and by a respective additional rubber spring having a large spring constant for limiting the angular displacement of the vehicle body.
A disadvantage of this known vehicle is that although, when equipped with a fully symmetrical damping device comprising compression coil springs and rubber springs between the vehicle body and the casters, a pronounced forward dipping of the vehicle body is prevented, the vehicle is nevertheless unsuitable for operation on a standard industrial floor having relatively great irregularities, since the total suspension or shock absorbing action is inadequate.